The reason why electricity can be used by people is largely because of insulation, that is, the use of non-conductive materials to isolate or wrap charged objects to prevent electric shock accidents. The outer isolation is called an insulator. The ideal insulator is non-conductive. In fact, insulators always have a certain conductivity. When high voltage is applied, a small amount of leakage current will pass. The ability of insulators to prevent current from passing is called insulation resistance. Insulation resistance testing is to measure the resistance between the conductor and the insulating layer. The measuring instrument used is called an insulation resistance tester.

In order to find leakage in the piping system, it needs to be pressurized. Since the leakage is most likely to be found when the water pressure is high, the tap water cannot be turned off to check for leakage. However, the available tap water can be restricted so that it can be detected Large leaks will not spray too much water around. The ideal test is to provide a limited amount of water under high (but not particularly high) pressure. The insulation tester (megohmmeter) will be on the insulation system. Apply a DC voltage and measure the resulting current, so that the resistance value of the insulation (the degree to which the insulation confines the current in the wire, or the degree to which it prevents current leakage) can be calculated and displayed.